Front fan retention in dual internal fan alternator

ABSTRACT

An alternator has a pole segment with a collar, an axially outward surface, and at least one key extending radially outward from the collar along the surface. A fan has a keying slot extending radially outward from a center ring, and a fan body including protrusions. The fan is mounted to the segment whereby the collar fits inside the ring and the key fits inside the keying slot, and the fan is welded to the segment at the protrusions. A method includes securing a fan to a pole segment by mating a radially-extending key formed on the segment to a keying slot of the fan and by welding the fan to the segment.

BACKGROUND

The present invention is directed to improvement of electric machines and, more particularly, to an improved fan assembly of a dual internal fan alternator.

An automotive alternator typically converts mechanical energy being supplied by a motor to electrical energy for charging a battery and powering a vehicle's electrical system when the motor is running. The alternator may contain substantially all of its components inside a housing. For example, an alternator outputs an alternating current (AC) voltage to a set of rectifier diodes that convert the AC voltage to a direct current (DC) voltage. Additional electrical and electronic components (e.g., voltage regulator or ECU) may be provided within the alternator housing, and such components create heat. Eddy currents, core losses, and electrical resistances of brushes and rotor and stator coils create additional heat. The mechanical operation of an alternator further creates heat as a result of friction.

A field current may be supplied as an electrical input to the rotor windings by slip rings, and one or more DC voltages are output from the diode rectifiers. To provide a direct current output with low ripple, a three-phase stator winding may be used and the pole-pieces of the rotor may be shaped (e.g., claw-pole) to produce an AC stator output waveform similar to a square wave instead of a sinusoid. A claw-pole rotor core is typically formed with a drive end (DE) core piece and a slip ring end (SRE) core piece, where the respective poles of the two rotor core pieces are formed as opposed fingers interleaved with one another. In an alternative application, an alternator may be configured as a DC generator having a commutator.

Modern automotive alternators are generally required to supply ever-greater amounts of electrical current. For example, hybrid and electric vehicles may use electricity instead of internal combustion for driving the wheels, and an alternator may be combined with a starter in a mild hybrid configuration such as in a belt alternator starter (BAS) system. Other electrical loading from air conditioning, electric power steering, and other vehicle systems further increases the required alternator electrical capacity.

Efficiency of automotive alternators is generally limited by fan cooling loss, bearing loss, iron loss, copper loss, and the voltage drop in the diode bridges. The use of permanent magnets may increase efficiency by providing a more constant magnetic field and by guiding flux between rotor windings. An alternator may have dual internal fans to improve operating efficiency and durability and to reduce heat-related failures. The alternator housing may have air intake and exhaust apertures adjacent respective rear and front fans, thereby providing a cooling air flow. However, the fan portions of automotive alternators are not optimized for structural integrity.

SUMMARY

It is therefore desirable to obviate the above-mentioned disadvantages by providing a structure and method for improving the structural integrity of an alternator having dual internal fans.

According to an exemplary embodiment, an alternator having a center axis includes a drive end (DE) segment having a raised collar portion, a plurality of claw poles, an axially outward segment surface connecting the claw poles, and at least one key extending radially outward from the collar along the segment surface. The alternator also has a fan having an inside diameter formed as a ring, a keying slot extending radially outward from the ring, a plurality of blades, and a fan body connecting the blades and including a plurality of protrusions. The fan is mounted to the segment so that the collar fits inside the ring and the key fits inside the keying slot, and the fan is welded to the DE segment at the protrusions.

According to another exemplary embodiment, a method of cooling an alternator includes providing a drive end (DE) segment having a raised collar portion, a plurality of claw poles, an axially outward segment surface connecting the claw poles, and at least one key extending radially outward from the collar. The method also includes providing a fan having an inside diameter formed as a ring, a keying slot extending radially outward from the ring, a plurality of blades, and a fan body connecting the blades and including a plurality of protrusions. The method further includes placing the fan onto the segment so that the collar fits inside the ring and the key fits inside the keying slot, and welding the fan to the segment at the protrusions.

According to a further exemplary embodiment, a method of assembling a rotor of an alternator includes securing a fan to a drive end (DE) pole segment by mating a radially-extending key formed on the segment to a keying slot of the fan and by welding the fan to the segment.

The foregoing summary does not limit the invention, which is defined by the attached claims. Similarly, neither the Title nor the Abstract is to be taken as limiting in any way the scope of the claimed invention.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic view of an electric machine;

FIG. 2 illustrates an exemplary twin internal fan configuration and airflow resulting therefrom, in the exemplary electric machine of FIG. 1;

FIG. 3 is an exploded perspective view of a fan aligned for mounting to a pole segment, according to an exemplary embodiment;

FIG. 4 is a schematic sectional view of a fan;

FIG. 5 is a perspective view of a key extending from the collar of a pole segment of an alternator, according to an exemplary embodiment;

FIG. 6 is a perspective view of a keying slot of a fan, according to an exemplary embodiment;

FIG. 7 and FIG. 8 are respective inward- and outward-facing perspective views of a pole segment assembly;

FIG. 9 is a partial sectional view taken along the line IX-IX of FIG. 7; and

FIG. 10 is a perspective partial view of an electric machine, according to an exemplary embodiment.

Corresponding reference characters indicate corresponding or similar parts throughout the several views.

DETAILED DESCRIPTION

The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of these teachings.

FIG. 1 is a sectional view of an exemplary electric machine 10 having a rotor assembly 15 that contains several components including a shaft 14, a field winding 3, and pole segments 1. A case 16 encloses the machine's components and includes a front bracket or drive end frame 18 and a rear bracket or slip ring end (SRE) frame 20, which may be made of aluminum. Case 16 secures a stator 4 to an inner wall surface of case 16. Shaft 14 is rotatably supported by front bracket 18 via a first bearing 19 and by rear bracket 20 via a second bearing 21. A pulley 22 is fixed to a first end of shaft 14, enabling rotational torque from an engine to be transmitted to shaft 14 by a belt (not shown). Slip rings 24 and associated electrical conductors are provided for supplying an electric current to rotor assembly 15. Slip rings 24 are fixed to an end portion of shaft 14, and a pair of brushes 26 are housed in a brush holder 28 disposed inside case 16 so as to slide in contact with slip rings 24 to pass the electric current therethrough. A voltage regulator (not shown) may be provided for adjusting the magnitude of an alternating voltage generated in stator 4. A first fan 34 and a second fan 36 are fixed to respective first and second axial ends of the rotor assembly 15.

FIG. 2 is a sectional view of the electric machine of FIG. 1, illustrating an exemplary twin internal fan configuration and airflow resulting therefrom. Respective front-end and rear-end air intake apertures 80, 81 are disposed in respective axial end surfaces of front bracket 18 and rear bracket 20, and front-end and rear-end air discharge apertures 82, 84 are respectively disposed in first and second outer circumferential portions of front bracket 18 and rear bracket 20. For example, the discharge apertures may be adjacent to exposed conductor end turns 38 that extend axially from stator core 4. The drive end, or first, fan 34 pulls air, generally shown with arrows 67, axially into electric machine 10 through inlet port 80 of front bracket 18. Most of the air is exhausted in a radial direction, indicated with arrows 68, out of electric machine 10 through outlet port 82 of the front bracket 18. Another part of the air flow may continue in an axial direction 69 and then exit out in a radial direction generally shown at 69′, flowing out through outlet port 84 of the rear bracket 16. On the SRE side, air is drawn into the back of electric machine 10 by second fan 36 in an axial direction indicated generally with arrows 70 and is then exhausted primarily in a radial direction indicated generally with arrows 70′, flowing out through outlet port 84.

In operation, when rotor 15 is rotated by an external driving force via pulley 22, a magnetic field is generated by the field winding 3 surrounding the field core, and the magnetic field passes circumferentially through the stator winding in conformance with the rotor rotation. Fans 34, 36, fixed to shaft 14, are rotated together with the field core, and blades 76 formed as cut-raised portions extending from fans 34, 36 are also rotated to produce cooling air flow inside electric machine 10.

FIG. 3 is an exploded perspective view of a fan 5 aligned for mounting to a pole segment 6, according to an exemplary embodiment. The collar 7 of segment 6 is an annular, raised portion having a center aperture 8 for receiving a shaft. A radially extending key 9 may be integrally formed with pole segment 6 as a portion raised from axially outward surface 11. Fan 5 has an annular mounting ring 2 with a radially inward surface 12. Fan 5 also has a keying slot 13, and a number of dimples 17 spaced circumferentially around fan surface 23. Fan 5 may be formed, for example, by first stamping a sheet steel material such as carbonize steel having corrosion resistance, and then bending the stamped work piece to form fan blades 25. Alternatively, fan 5 may be cast of steel or other suitable material. Fan blades 25 may vary in number, height, shape, size, and angle, and they may be curved or straight. The assembly includes placing fan 5 onto collar 7 and then press fitting key 9 into keying slot 13. As a result, fan inside surface 12 is placed around at least a portion of the radially outward surface 27 of collar 7. Typically, embodiments have at least two keys 9 and the same number of keying slots 13, and such are arranged symmetrically about collar 7. For example, two keys 9 may be 180° apart, three keys 9 may be 120° apart, four keys 9 may be 90° apart, etc. The multiple keys 9 and associated keying slots 13 are also typically the same shape and size, so that the rotating assembly is substantially balanced and symmetrical. After fan 5 has been pressed onto segment 6, it is then welded in place and is further pressed against segment 6 during the welding.

FIG. 4 is a schematic sectional view of a fan 5. When dimples 17 are formed by stamping the outer fan surface 29, projections 30 are thereby formed on inner fan surface 31. When fan 5 is pressed onto pole segment 6, projections 30 are thereby pressed against axially outward pole segment surface 11. A welding electrode (not shown) is attached to fan 5 and an opposite polarity welding electrode is attached to pole segment 6. When electric current of the welding flows between the electrodes, the resistance at the interfaces of projections 30 and surface 11 creates heat at the interfaces, and projections 30 are melted so that welds are formed at the interfaces. The welding electrodes or other apparatus may be used to urge fan 5 and segment 6 together during the welding process, and brazing or other filling process may be utilized for removing spaces or voids between the welded surfaces. For example, the electrodes may provide clamping pressure and/or impacting force while passing a current of 5000 to 100,000 amperes, at a voltage of 3.0 to 10.0 volts, with a duration of less than two seconds and a duty cycle of five to ten percent. Any other suitable electric current may be utilized, depending on a particular application. For example, high frequency brazing/welding may be utilized when only a shallow depth weld is required. Impacting and clamping surfaces may be chosen for aligning the interfacing surfaces, for applying pressure to develop proper surface resistance, for containing molten metal, for forging the interfacing material, for transferring electric current, for dissipating excessive heat, and/or for cooling (e.g., by being water cooled). Processing may include post weld heat cycling, and impacting and/or pressure forging performed at any time. For example, a softening current may be applied, followed by an impacting that compresses the softened metal. A concurrent or subsequent impacting of fan 5 in proximity to the softened interface acts to produce a higher degree of coalescence or intimate joining by metallurgical union. Brazing material may be applied to interface locations of pole segment surface 11 by sputtering to prevent contamination, oxidation, and other potential problems, although plating, vapor deposition, or another process may alternatively be used. By way of non-limiting example, a brazing material may include silver, phosphorous, silicon, copper, nickel, tin, aluminum, magnesium, gold, zinc, cadmium, and various alloys known in the art and typically chosen depending on melting temperature range and flow properties at high temperature. In contrast to conventional brazing, a flux, and subsequent removal of its residue, may be unnecessary when the brazing material already uniformly covers the interface area and when the brazing material is being provided for localizing heat rather than for being distributed by capillary action.

FIG. 5 is a perspective view of key 9 and FIG. 6 is a perspective view of keying slot 13. Key 9 is formed as an integral part of collar 7 which, in turn, may be formed as an integral portion of pole segment 6. For example, a unitary pole segment 6 may be formed in a high temperature forging process. Key 9 may be integrally formed with pole segment surface 11 or it may alternatively be axially offset therefrom. A substantially oval depression 32 is formed in segment surface 11, at a location aligned with and radially outward of key 9. Depression 32 may be used, for example, to provide access for a tool (not shown) for applying force during press fitting to a proximate portion 33 of fan surface 23 and/or to provide a depository for any weld nugget or other substance such as brazing material that might interfere with the mating between key 9 and keying slot 13. For example, slot 13 includes opposed axially extending tabs 35, 37 that respectively press against and secure the lateral sides 39, 40 of key 9. By creating space around such interface, the welding/brazing materials are prevented from interfering. In addition, the space allows for dimensional tolerances of key 9. For example, the space around depression 32 may be utilized for radially positioning DE fan 5. The extra space of keying slot 13 includes an aperture 41 through fan center ring 2. By creating space around key 9 and fitting tabs 35, 37, keys 9 of the assembled structure act to prevent circumferential movement of fan 5, with respect to segment 6, without incurring undesirable axial or radial interference at the keying interface. The extra space assures that welding does not occur at the keying structures.

FIG. 7 and FIG. 8 are respective inward- and outward-facing perspective views of a pole segment assembly 42, and FIG. 9 is a partial sectional view taken along the line IX-IX of FIG. 7. Assembly 42 is shown having only one key 9, but typically has at least two keys arranged symmetrically. Fan 5 is secured to pole segment 6 by the joinder of key 9 with fan keying slot 13 (FIG. 6) and by welding at locations of dimples 17. Collar 7 has an exposed collar portion 43 that extends axially beyond fan ring 2. Fan 5 is typically not press fit against collar 7, and some space exists between fan ring 2 and annular collar surface 27 (FIG. 5). Such annular space allows the circumferential torque on fan 5 to be concentrated at keys 9.

The projection welding of assembly 42 may use very high current in short duration pulses, and a brazing material with thermally conductive additives may be used for filling gaps between fan 5 and segment 6. By comparison, conventional alternators may use TIG or laser welding to avoid a high temperature causing the degaussing of an alternator's permanent magnets. However, by separately manufacturing assembly 42, this conventional problem is avoided. The contacting metal surfaces of fan 5 and segment 6 are joined by the heat obtained from resistance to electric current flow. The surfaces may be held together under pressure exerted by welding electrodes (not shown). For example, copper alloy electrodes urge fan 5 and segment 6 together while simultaneously forcing a large current through projections 30, thereby melting the metal and forming welds. Heat is concentrated at projections 30, which permits the welding of the relatively heavier pole segment 6 and localizes the welds at projections 30. Any appropriate number of projections may be formed on fan 5, such as for closely spacing the individual welds. Projections 30 may also be utilized for positioning the workpieces. The welding electrode(s) are typically placed at or near dimples 17 so that the welding current is concentrated at underlying projections 30. When current pulses have a high magnitude and a short duration, the welds may be somewhat isolated to the general areas surrounding the respective projections 30. Keys 9 and keying slots 13 are thereby somewhat isolated from the welding.

A winding core section 44 may be formed as an integral part of pole segment 6, or it may be a separate component. In an alternative embodiment, the interior portion of pole segment 6 may include recessed portions 45, each circumferentially aligned with a key 9. For example, it may be desirable for the thickness of pole segment 6 to be uniform around its circumference, and the increased thickness of segment 6 at the raised keys 9 may be offset by reducing segment thickness under keys 9 by forming recess 45.

In FIG. 9, an exemplary sectional profile illustrates how key 9 may be formed integrally with pole segment 6. Key 9 may have a stepped profile in a radially outward direction, whereby a portion of radially outward surface 27 of collar 7 extends axially outward of key 9. The radially outward portion of key 9 may extend axially inward of a nominal fan resting surface 31. For example, fan surface 31 abuts pole segment surface 11 after the welding process, and depression 32 prevents any binding around key 9 so that fan surface 31 may lie flush against segment surface 11. When properly seated, the axially outward side of key 9 is slightly axially inward of fitting tab 35 and fitting tab 37 (FIG. 6), and the radially outward end of key 9 is slightly spaced apart from fan portion 33.

The interface of fan surface 31 and pole segment surface 11 may include applied or injected resin, nylon, adhesive, or other suitable thermally conductive material. The added material may provide a more stable and integral structure, may assist in balancing, and increases heat transfer out of the rotor core. Material(s) other than those used in brazing may be injected or otherwise applied to gaps and spaces in the fan/segment interface that remain after the welding process. For example, a curable thermally conductive material may be applied to segment surface 11 and/or fan surface 31 before welding, whereby the compression of surfaces 11, 31 against one another during welding causes the applied material to fill such gaps and spaces. The welding of projections 30, the press fitting of key slot 13 onto key 9, and the flow of filler material into unwelded gaps may occur simultaneously during manufacture when the welding electrodes act to clamp surfaces 11, 31 together, when a filler material is pre-applied to at least one of surfaces 11, 31, and when key slot 13 is properly seated as a result of the electrode compression or by other clamping.

FIG. 10 is a perspective partial view of an electric machine 46, according to an exemplary embodiment. Fan 5 is secured to DE pole segment 6 as described hereinabove. The rotation of shaft 14, segment 6, and fan 5 creates a circumferential force between segment 6 and fan 5, in parallel with the rotational direction 47, usually but not always clockwise. Such circumferential force varies with the changes in rotational speed and is affected by the resistance to the corresponding movement by fan blades 25. As a result of acceleration and fan blade resistance, rotational torque on fan 5 is imparted onto keys 9. The tight fit of keys 9 with corresponding keying slots 13 provides a centering function for DE fan 5 and also prevents fan 5 from rotating relative to pole segment 6. Increasing the widths, lengths, and heights of keys 9 acts to distribute the shear stresses imposed thereon. Typically at least two or three keys 9 are provided to further distribute shear stresses, and to prevent relative radial movement of fan 5 respecting segment 6. Axial movement of fan 5 relative to segment 6 is prevented by the welds at the axially inward fan projections 30 (FIG. 4) that are aligned with dimples 17.

The exemplary embodiments describe structure and methods of assembling a rotor of an alternator that include securing a fan to a drive end (DE) pole segment by mating a radially-extending key formed on the segment to a keying slot of the fan and by welding the fan to the segment. In alternative embodiments, one or more keys may be formed on a fan and corresponding keying slots may be formed on a pole segment. However, in such a case, welding at the keying interfaces is carefully controlled to assure that distortion of the fan and/or over-welding of fan portions at the projections does not occur.

While various embodiments incorporating the present invention have been described in detail, further modifications and adaptations of the invention may occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention. 

What is claimed is:
 1. An alternator having a center axis, comprising: a pole segment having a collar, a plurality of claw poles, an axially outward segment surface connecting the claw poles, and at least one key extending radially outward from the collar along the segment surface; a fan having an inside diameter formed as a ring, a keying slot positioned radially outward from the ring, a plurality of blades, and a fan body connecting the blades and including a plurality of protrusions; wherein the fan is mounted to the segment so that the collar fits inside the ring and the key fits inside the keying slot, and wherein the fan is welded to the segment at the protrusions.
 2. The alternator of claim 1, wherein the at least one key comprises a plurality of keys symmetrically arranged about the center axis and the keying slot comprises a corresponding plurality of slots aligned with the keys and mated thereto.
 3. The alternator of claim 2, wherein the protrusions are symmetrically arranged about the center axis.
 4. The alternator of claim 1, wherein the keying slot comprises a pair of opposed axially-extending tabs.
 5. The alternator of claim 1, wherein the key is mated to the keying slot by an interference fit.
 6. The alternator of claim 1, wherein the collar is formed as an integral part of the segment.
 7. The alternator of claim 1, wherein the protrusions are formed on an axially inward surface of the fan body.
 8. A method of cooling an alternator, comprising: providing a pole segment having a raised collar, a plurality of claw poles, an axially outward segment surface connecting the claw poles, and at least one key extending radially outward from the collar; providing a fan having an inside diameter formed as a ring, a keying slot positioned radially outward from the ring, a plurality of blades, and a fan body connecting the blades and including a plurality of protrusions; placing the fan onto the segment so that the collar fits inside the ring and the key fits inside the keying slot; and welding the fan to the segment at the protrusions.
 9. The method of claim 8, wherein the welding comprises brazing an interface of the fan and the segment.
 10. The method of claim 8, further comprising placing a thermally conductive material at an interface of the fan and the segment.
 11. The method of claim 8, wherein the welding comprises axially clamping the fan and segment toward one another.
 12. The method of claim 8, wherein the keying slot includes a pair of axially extending tabs that engage the key, whereby the key is substantially isolated from the remainder of the fan.
 13. The method of claim 12, wherein the welding comprises placing a welding electrode proximate the protrusions to thereby substantially isolate the welding to the protrusions.
 14. The method of claim 13, further comprising filling gaps between isolated welds with a thermally conductive material.
 15. The method of claim 8, wherein the key is secured inside the keying slot by press fitting.
 16. The method of claim 15, wherein the welding and the press fitting are substantially simultaneous.
 17. A method of assembling a rotor of an alternator, comprising securing a fan to a drive end (DE) pole segment by mating a radially-extending key formed on the segment to a keying slot of the fan and by welding the fan to the segment.
 18. The method of claim 17, wherein the fan has an axially inward surface containing a plurality of projections, and wherein the welding comprises projection welding.
 19. The method of claim 17, wherein the welding comprises brazing.
 20. The method of claim 17, wherein the mating comprises press fitting a plurality of the radially-extending keys to a corresponding plurality of the keying slots. 